The present invention relates to a method of making a profiled work of aluminum or aluminum alloy by extruding process.
Recently, profiled works of aluminum or aluminum alloy of various configurations in cross-section produced by extruding process have been increasingly made important in the construction works such as buildings, engineering works, vehicles and the like.
The most important problem in manufacturing profiled works of aluminum or aluminum alloy by extruding process lies in the improvement in the extruding velocity in mass production of the profiled works while superior quality of the surface of the profiled work is maintained.
However, when a billet of aluminum or aluminum alloy is extruded through an extruding machine so as to produce a profiled work, frictional heat generated between the bearing surface of the extruding die and the mass of the billet flowing along the bearing surface of the die increases as the extruding velocity is raised, so that the material of the billet tends to stick to the bearing surface of the die thereby deteriorating the surface condition of the bearing surface and resulting in surface defects formed in the surface of the extruded profiled work. Thus, the upper limit of the extruding velocity is necessarily set at a certain value and it is extremely difficult to raise the extruding velocity beyond the thus set upper limit without causing any surface defects of the profiled work.
In order to avoid the above described sticking of material of the billet to the bearing surface of the extruding die during the extruding process, it has been proposed to include a little quantity of element B in the billet.
By such a measure, however, the content of B to be included in the billet must be greater than 0.01% by weight and, preferably, greater than 0.03% in order to achieve satisfactory results. A billet of aluminum or aluminum alloy containing such a large amount of B tends to absorb excessive gas during the casting procedure of the billet so that it is not only difficult to obtain satisfactory profiled works having sound mechanical properties from such a gas including billet but also the profiled works produced from such a billet tends to cause local decolorizations of the surface of the profiled work on account of the presence of B component when it is subjected to anodic oxydation treatment so that local colorless spots are generated in the colored surface of the anodized film formed on the profiled work by the anodic oxidation treatment, thereby deteriorating the surface quality of the product and increasing the percent defective of the products.
The present invention aims at avoiding the above described disadvantages of the prior art method of making a profiled work of aluminum or aluminum alloy by extruding process.